Method for reducing edge cracking during rolling of metal shapes



Nov. 11, 1969 E. I. VALYI 3,477,271

METHOD FOR REDUCING EDGE CRACK DURING ROLLING OFMETAL SHAP Filed July 31, 1967 FIG. 1

v FIG. 5

3| FIG. 4

1 NTOR EMER VALYI ATTORNEY United States Patent U.S. Cl. 72-365 3 Claims ABSTRACT OF THE DISCLOSURE The method of reducing the loss of metal due to edge cracking which occurs during the rolling of metal shapes wherein one or a pair of grooves is formed in the sides of the metal shape adjacent the edges thereof to form lines of weakness. During rolling, any edge cracks extend only 'to this line of weakness. After rolling, the edge portions are trimmed off along these lines of weakness to leave the body of the metal shape free of edge cracks.

This invention relates to the rolling of metals and has for an object to reduce the waste of metal which results from edge cracking during the rolling operations.

Edge cracking in rolling is a well known phenomenon leading to appreciable losses of metal and giving rise to numerous secondary operations between steps of the rolling process. Edge cracking occurs particularly during hot rolling of hot-short alloys, i.e. alloys whose ductility is substantially reduced at the temperature of rolling.

The effects of hot-shortness are manifest even in so called cold rolling operations. Even if the material being cold rolled is not preheated in bulk prior to rolling, the deformation of cold rolling alone may elevate the temperature of the metal into the hot-short range of the respective alloy.

As an example, aluminum alloys with a magnesium content in excess of 5% show marked hot-shortness and so do many other alloys that are normally rolled. Edge cracking may penetrate to the extent of 20% of the rolled strip width. In order to minimize it, edge trimming and shearing operation are interjected between rolling passes to remove material that has commenced to crack. Alternately, elaborate rolling mills, employing multiple rolls are used to minimize edge cracking, but even here, with very hot-short alloys, edge cracking is not prevented.

The present invention concerns a method to prevent.

edge cracking by introducing a predetermined region of weakness into the ingot and strip and by directing such cracks as may tend to occur during rolling to follow such lines of weakness, rather than to propagate randomly throughout the strip. It is known, as for example described in US. Patent No. 3,092,470, that notches applied to the outside surface of an ingot before rolling and then treated with a material which prevents the welding of these notches will produce a residual line-notch upon rolling which represents a region of substantial weakness in the finished strip. The above mentioned patent proposes to use the process of weakening ingots in this manner to effect separation of laminated strip between accurately placed laminations.

The method of rolling metal according to the present invention concerns the application of notches or areas of weakness in the ingot, or in the pre-rolled plate prior to final rolling, whereby care is taken to prevent these notches from closing up by welding under the pressure of the subsequent rolling steps.

3,477,271 Patented Nov. 11, 1969 The invention will be better understood from the following description, taken in connection with the accompanying drawing, in which a specific embodiment has been set forth for the purposes of illustration.

In the drawing:

FIG. 1 is a plan view of an ingot prior to rolling illustrating the position of the weakening notches for controlling edge cracking; and

FIG. -2 is a transverse section taken on the line 22 of FIG. 1; and

FIG. 3 is a broken plan view showing an edge portion of the ingot after the rolling; and

FIG. 4 is a transverse similar section taken along the line 44 of FIG. 3; and

FIG. 5 is a similar section through the metal shape after trimming.

Referring to the drawing more in detail FIG. 1 illustrates a metal shape such as a billet or ingot, as usually provided for rolling, except for the features to be described below.

In accordance with the present invention upper and lower grooves 12 and 13 respectively are formed in the upper and lower surfaces 14 and 15 of the ingot. These edge grooves are disposed as close to the side edges of the ingot 10 as feasible and extend inwardly for a substantial distance such as about one third of the thickness of the ingot. The upper and lower grooves 12 and 13 are preferably in vertical registration and form a line of weakness extending along both side edges of the ingot.

In order to prevent the sides of the grooves from welding together during the hot rolling steps the side walls thereof are coated with a weld preventing material as described, for example, in the above mentioned U.S. patent.

The ingot 10 is subjected to the usual steps of hot and cold rolling for materially reducing the thickness thereof and extending the same in length so as to form a thin metal strip 20 as illustrated in FIGS. 3-5. Edge grooves 21, while reduced in thickness retain substantially the same relative proportion of the total thickness of the strip. Any edge cracks which occur during the rolling operations will extend only to the line of weakness formed by the notches produced from grooves 21 and then propagate along the line of weakness of those notches instead of extending further into the body of the strip 20.

The strips 20 are now trimmed along the lines of weakness formed by the grooves 21, thereby removing the defective edge portions containing the edge cracks and leaving the body of the strip intact. The trimmed strip 31 is illustrated in FIG. 5, in which the waste of metal due to edge cracking is reduced to a minimum, due to the operations here described.

What is claimed is:

1. The method of reducing the loss of metal due to edge cracking during the rolling of a metal ingot under conditions to materially reduce the thickness thereof to form a metal strip with a corresponding extension in length, which method comprises forming a longitudinal groove in at least one surface of the ingot adjacent a side edge thereof prior to rolling, incorporating in said groove an anti-weld material capable of preventing the sides thereof from welding together during the subsequent rolling operations, subjecting the ingot to a series of hot and cold rolling steps adapted to form said metal strip therefrom whereby any edge cracks which are produced as the metal passes through its hot-short range terminate in the zone of said groove, and thereafter trimming the edge of said strip in the zone of said groove 3 to thereby remove therefrom the area containing such edge cracks.

2. The method set forth in claim 1 in which a pair of longitudinal grooves are disposed in the upper and lower surfaces of said metal ingot adjacent each side edge thereof.

3. The method set forth in claim 2 in which each of said grooves extends in depth to about a third of the thickness of the metal ingot.

4 References Cited UNITED STATES PATENTS 6/1943 Ripling 72-3 65 6/1964 Werthman 72l99 

